1. Technical Field
The invention relates to a method for the wet treatment of laundry items with the laundry being at least washed in a rotary driven drum.
2. Prior Art
Employed for the wet treatment of laundry items, particularly in commercial laundries, are so-called continuous tunnel washing machines which have a rotary driven drum which revolves about a preferably horizontal center axis. In the elongate drum, laundry items are, in a continuous pass, washed, rinsed and if necessary subjected to other treatment, in particular aftertreatment. The drum is driven in a preferably rotating, circulatory manner, thus executing complete circular movements during the wet treatment of the laundry. Arranged in the drum are built-in elements, in particular paddle blades. Permanently fixed in the drum, the paddle blades turn in the circumferential direction of the drum, thus serving to carry along the laundry within the drum and, according to need, to transport the laundry through the drum in its longitudinal direction.
During part of each revolution of the drum, the laundry lies in front of the paddle blades as well as upon the inner side of the drum. When, during the rotational actuation of the drum, the off-center paddle blades within the drum reach or pass through an upper cusp point (apex), the laundry drops into the interior of the drum due to gravity. This results in the laundry being thrown off the paddle blades and the inner side of the drum shell.
In order to increase the handling performance of tunnel washing machines, one aims at propelling the drum at the highest possible frequency of rotation, thus causing the drum to rotate at a correspondingly high speed. With increasing speed or rotational frequency, the laundry, particularly due to centrifugal forces, tends to adhere to the paddle blades and to the surfaces of the drum shell. This means that the laundry does not completely drop off when the paddle blades pass through the apex point in the drum. Having the laundry thrown off and drop down is essential for an effective washing and/or rinse cycle. Therefore, even incomplete throwing off and dropping down of the laundry results in a reduced intensity of the treatment; in particular, there is a drop in performance in washing and/or rinsing. The greater rotational frequency or driving speed of the drum thus becomes practically ineffective.
Proceeding from the above, the invention is based on the problem of creating a method for a more effective and efficient wet treatment of laundry.
A method for solving this problem is characterized in that the drum is driven with different rotational frequencies. By having the drum driven at different rotational frequencies (in other words: different rotary frequencies or different number of revolutions), its rotational speed can be varied to meet these requirements. The disadvantages posed by driving the drum at a higher rotational frequency can be eliminated by a temporary or intermittent reduction of the rotational frequency. The faster drum drive speed at all other times can thus fully exploit the advantages of the drum action.
The drum is driven preferably in rotation, with the drum being driven at different rotational frequencies during at least some, preferably during all, of its revolutions. The drum is thereby driven with a different velocity profile during at least some of its revolutions, with slower drive speeds being selected when disadvantages arising from too rapid drive speeds may be encountered. The drum is driven more rapidly in those circumferential areas of the drum in which higher drive speeds do not have a disadvantageous effect on the performance of treatment, in particular concerning washing and/or rinsing efficiency, which on the whole makes it possible to achieve a greater efficiency in treatment using tunnel washers.
Pursuant to a preferred method, the drum is driven at a plurality of, preferably two, different rotational frequencies during a respective revolution, with each frequency being held essentially constant during its segment of the drum revolution. Accordingly, the drum runs at the same speed in the respective area, which results in an even wet treatment of the laundry.
It is also provided that the drum is to be braked or accelerated between the drive phases of the drum by means of applying a lower or higher rotational frequency, respectively. This gives a stepped velocity profile, with the phases of drum acceleration or braking serving to attain a higher or lower rotational frequency and/or circumferential speed (in other words: rotational speed) of the drum. In particular, braking the drum from the higher circumferential frequency to the lower circumferential frequency applies a impetus force on the laundry, which facilitates the loosening of the laundry from the drum and the paddle blades, and in particular ensures a more effective and above all more complete throwing off of the laundry.
According to a further proposal of the invention, the drum is driven with the higher rotational frequency over a greater segment of its circumference that with the lower rotational frequency. This keeps the reduction of the drum drive speed to a minimum but at the same time retains to the maximum possible degree the performance advantage offered by the higher circumferential speed of the drum.
It is furthermore provided that when built-in elements of the drum, in particular paddle blades for carrying along the laundry, reach an upper region of reversed direction (apex) of the drum, the drum is driven at a slower circumferential speed or rotational frequency. Accordingly, the drum is driven more slowly as the laundry is thrown off and this reduces the centrifugal forces which might otherwise hold the laundry to the paddle blades and inner side of the drum shell. This results in an effective and in particular complete throwing off of the laundry in that it can loosen more easily from the inner walls of the drum and the paddle blades due to the lower circumferential speed of the drum.
Pursuant to a preferred embodiment of the method, when the paddle blades reach the upper reverse area of the drumxe2x80x94or even shortly before thatxe2x80x94the drive of the drum is braked enough for the drum to shift from the higher rotational frequency to the lower rotational frequency. This braking action gives the laundry a dynamic impetus which favors its loosening from the paddle blades and the inner side of the drum wall, thus ensuring a reliable throwing off of the entire laundry at the apex of the drum. This not only represents an improvement in the efficiency of throwing off laundry at the apex region of blade motion by reducing the circumferential speed of the drum. This also favors and enhances the reliable throwing off of laundry by the braking of the drum required for reducing its rotational speed.